Process for making agglomerates from coal using coal extract as binder

ABSTRACT

A PROCESS FOR MAKING AGGLOMERATES FROM NON-CAKING OR WEAKLY CAKING COALS WHICH INCLUDES TUMBLING IN A ROTARY KILN, AT AN ELEVATED FORMING TEMPERATURE, CARBONACEOUS MATERIAL OBTAINED FROM THE COAL FEEDSTOCK AND A BINDER ALSO OBTAINED FROM THE COAL FEEDSTOCK TO FORM GREEN AGGLOMERATES. THE BINDER CONTAINS A NONDISTILLABLE COAL EX-   TRACT FRACTION WHICH IS FLUID AT THE FORMING TEMPERATURE IN THE KILN. THE NONDISTILLABLE COAL EXTRACT FRACTION IS OBTAINED BY SOLVENT EXTRACTION OF THE COAL FEEDSTOCK.

Feb. 9, 1971 E. GORIN 3,56

PROCESS FOR MAKING AGGLOMERATES FROM COAL USING COAL EXTRACT AS BINDER Filed March 20, 1967 2 Sheets-Sheet 2 FIG. 2

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EVERETT GORIN United States Patent Oil-ice 3,562,783 Patented Feb. 9, 1971 3,562,783 PROCESS FOR MAKING AGGLOMERATES FROM COAL USING COAL EXTRACT AS BINDER Everett Gorin, Pittsburgh, Pa., assignor to Consolidation Coal Company, Pittsburgh, Pa., a corporation of Delaare Filed Mar. 20, 1967, Ser. No. 624,472 Claims priority, application Great Britain, Mar. 20, 1966, 13,571/ 66 Int. Cl. Cb 53/08 US. Cl. 201-6 8 Claims ABSTRACT OF THE DISCLOSURE A process for making agglomerates from non-caking or weakly caking coals which includes tumbling in a rotary kiln, at an elevated forming temperature, carbonaceous material obtained from the coal feedstock and a binder also obtained from the coal feedstock to form green agglomerates. The binder contains a nondistillable coal extract fraction which is fluid at the forming temperature in the kiln. The nondistillable coal extract fraction is obtained by solvent extraction of the coal feedstock.

This invention relates to the production of formcokev from non-caking or weakly caking coals, and, more particularly, to the production of a formcoke which is suitable for use in conventional blast furnaces. The process of this invention is an adaptation to non-caking or weakly caking coals of the process described and claimed in United States Patent 3,073,751 for the production of formcoke from caking bituminous coals.

The term formcoke is applied to coke which is obtained by the calcination of preformed or preshaped carbonaceous solids. The term is used to distinguish from coke obtained as broken pieces of all sizes and shapes from conventional coke ovens. There are many Ways, mechanically, of preforrning or preshaping carbonaceous solids, for example, by rollers, or by molds, that is, briquetting. However, the present invention is concerned particularly with the method of preforming which involves the use of a rotating, substantially horizontal, cylindrical kiln, that is, hot pelletizing. In such a kiln, the carbonaceous solids, in a plastic condition, are tumbled to form dis crete agglomerates or pellets of a generally spherical shape. These so-called green agglomerates may then be calcined to form formcoke, not only of predetermined size and shape, but also of great strength.

The carbonaceous solids used in the production of formcoke may be the different kinds of coal, including lignite, or they may be the solid distillation residues of coal, commonly called chars, or they may be mixtures of coal and char. Also, as we shall more fully describe later, they may include the carbonaceous solid residues from solvent extraction of coal. In order for these various and sundry carbonaceous solids to form green agglomerates in the rotary kiln, they must be, at least momentarily, in a plastic or sticky state. Such a plastic state or condition may be created by the extraneous addition of a binder or by the autogenous formation of a binder from the carbonaceous solid itself. Thus, in the case of highly caking bituminous coals, an adequate amount of suitable binder is produced autogeneously in the rotary kiln at the elevated temperature maintained during the formation of the agglomerates. No supplementary binder is needed. On the other hand, weakly caking coals require not only that binder which is produced autogenously in the kiln, but also that which may be obtained by low temperature carbonization of a portion at least of the coal prior to its introduction into the kiln. However, very weakly caking or non-caking coals do not provide suitable binder in adequate amount by such means. Accordingly, it has been necessary to resort to extraneous sources for the requisite binder in the amount desired. The cost of the formcoke process in the case of such weakly caking or noncaking coals has been accordingly higher.

The primary object of the present invention is to provide an improved process for making formcoke from a weakly caking or a non-caking coal, using only materials derived from the coal itself.

In accordance with the present invention, a suitable binder in adequate amount is provided for the formation in a rotary kiln of green agglomerates from a weakly caking or noncaking coal. The binder is derived in the following manner: the tar product obtained from the agglomerate formation step and from the calcining step is fractionated to yield a distillate tar fraction and pitch, which serves as a part of the binder required. The distillate tar fraction is mixed with at least a part of the feed coal at elevated temperature to form an extract and a solid residue. The residue is separated from the extract, and the extract is heated to separate solvent and tars. The binder may be characterized as a nondistillable tar fraction derived from the coal which is fluid at the forming temperature in the kiln, but which decomposes with time at forming temperatures to leave a substantial carbon residue.

FIGS. 1 and 2 of the drawings are schematic flow sheets of preferred embodiments of the present invention as applied to a non-caking coal and a weakly caking coal, respectively.

Referring to FIG. 1, a process which is adapted for use with non-caking coals, in contrast to Weakly caking coals, is schematically illustrated. In this process, preferably all the feed coal is subjected to pre-extraction with a solvent to yield an extract suitable as a binder. The numbers parenthetically associated in the figure with certain of the materials are illustrative of the material balance obtainable based upon the experimental work to date.

One hundred pounds of finely divided non-caking coal (on a moistureand ash-free basis, i.e., MAF) containing 8.31 pounds ash were introduced into a coal extraction zone 10 through a conduit 12. The function of the extraction zone is to split the coal into an extract and a solid carbonaceous residue by means of treatment with a coal solvent at elevated temperature, generally in the range between 350 and 400 C. At 380 C. for example, between 30 and 40 percent by weight of the feed coal may be obtained as extract. The particular procedure, however, for splitting the coal into extract and residue, is not of the essence so far as the present invention is concerned. Generally, it includes heating the coal in a closed retort with a solvent derived from the process itself, as will be seen. As much extract is produced as it is convenient to do so without the extraneous addition of hydrogen. Depths of extraction approaching 50 percent may be reached without such hydrogen addition.

The products of extraction, together with solvent, are transferred to a separation zone through a conduit 14. In this zone, the residue is separated from the extract by filtration or by centrifugation, for example. The extract, while still dissolved in the solvent, is conducted via a conduit 16 to a solvent recovery zone 20. In this zone, most of the solvent is recovered by distillation and recycled by a conduit 18 to the inlet pipe 12. Make-up solvent is added to the same inlet pipe as needed through a conduit 22. The separated extract, which is essentially nondistillable, amounting to pounds, together with 5.3 pounds of solvent which has polymerized to a nondistillable liquid due to its exposure to high temperature and by interaction with the coal, is transferred through a conduit 24 to a liquid binder feed pipe 26 leading to the agglomerating rotary kiln 25. Recycle pitch in the amount of 10.7 pounds derived in a manner to be described shortly is also conveyed by the same liquid binder feed pipe 26. Thus, a total of 51 pounds of binder is introduced into the kiln concurrently with char derived from the extract residue, as will now be described.

The residue recovered in the separation zone 15 is transported through a line 28 to a low temperature carbonization zone 30. This zone operates at about 925 F., its function being to convert the residue to char and tar. The char is transferred by a line 32 to a char heating zone 35 wherein the char is heated to a temperature of about 1200" F. by combustion with air introduced through a pipe 34. The hot char, in the amount of 57.5 pounds, is carried by a conduit 36 to the rotary kiln 25.

The rotary kiln 25 is adapted to rotate about its longitudinal axis and serves to tumble the hot char and pitch together as they advance through the kiln. The tempera ture of the char as introduced is selected so as to maintain the temperature of the tumbling mixture adiabatically at about 775 F. A full description of the operation of this kiln for the purpose of forming agglomerates is given in United States Patent No. 3,073,751. Green agglomerates having a predetermined size are withdrawn through an outlet pipe 38 and fed to a calcining zone 40 where they are heated to an elevated temperature sufiiciently high to remove substantially all volatile matter. The calcined product is withdrawn through a pipe 4. The amount so withdrawn is 64.1 pounds of formcoke on a moistureand ashfree basis. The formcoke contained 8.3 pounds of ash. Off-size agglomerates are recycled through a conduit 39 to the low temperature carbonization zone 30.

The solvent for the extraction of the coal in the extraction zone 10 is derived as follows: Tar is produced in the low temperature carbonization zone 30, the rotary kiln 26, and the calciner 40. This tar is conducted by conduits 42, 43, 44 and 45 to a tar recovery zone 46 where any gas is separated and discharged through a conduit 47. The tar itself is transferred via a pipe 48 to a fractionating still 50. The latter serves to split the tar into a light overhead distillate boiling below 230 C. and amounting to 4.4 pounds, a middle distillate portion boiling between 230 and 400 C. and amounting to 7.3 pounds, and lastly, a pitch fraction in the amount of 10.7 pounds. The middle distillate fraction supplies the make-up solvent for the extraction zone, while the pitch fraction is recycled directly to the kiln to act as binder.

Referring to FIG. 2 of the drawings, a process which is especially adapted for use with weakly caking coals, in contrast to non-caking coals, is schematically illustrated. The numbers used in FIG. 2, Wherever the same as in FIG. 1, designate the same or corresponding parts of the embodiment. Since the coal in this instance is weakly caking, it can supply part of the necessary binder autogenously in the kiln during the agglomerating step. Accordingly, it is not necessary to send all the coal to the extraction zone 10. A part is fed directly via a conduit into the kiln. 25 for admixture with char and the supplemental binder in the tumbling zone inside the kiln. An-

other part of the coal may also by-pass the extraction zone by transfer directly through a conduit to the low temperature carbonization zone 30 where it is carbonized along with extraction residue to yield char and tar. In the event more char is produced in the carbonization zone 30 than is needed in the process, the excess may be withdrawn through a conduit 33. The relative amounts f coal going to extraction and to carbonization are regulated to provide the necesssary binder in adequate quantities. Since carbonization is less expensive than extraction, it is desirable to use it to the extent possible, and still yield the proper binder. Otherwise, the process of FIG. 2 operates the same as that illustrated in FIG. 1.

According to the provisions of the patent statutes, I have explained the principle, preferred construction, and mode of operation of my invention and have illustrated and described what I now consider to represent its best embodiment. However, I desire to have it understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically illustrated and described.

I claim:

1. In the process of making agglomerates from a weakly or noncaking coal wherein a mixture of carbonaceous solids and carbonaceous binder is tumbled in a rotary kiln to yield agglomerates and tar, there being an inadequate amount of the requisite carbonaceous binder produced autogenously in said kiln, the improvement comprising subjecting at least a portion of said coal to treatment with a solvent at an elevated temperature to yield a coal extract containing a nondistillable fraction which is fluid at the forming temperature in the kiln, and introducing said nondistillable coal extract fraction into the kiln to serve as at least part of said carbonaceous binder for said carbonaceous solids.

2. In the process of making agglomerates from a weakly or noncaking coal wherein a mixture of carbonaceous solids and carbonaceous binder is tumbled in a rotary kiln to yield agglomerates and tar, there being an inadequate amount of the requisite carbonaceous binder produced autogenously in said kiln, the improvement comprising subjecting at least a portion of the feed coal to treatment with a solvent at an elevated temperature to yield a solid residue and a coal extract containing a non-distillable fraction which is fluid at the forming temperature in the kiln, separating said solid residue from said coal extract, introducing said nondistillable coal extract fraction into the kiln to serve as at least part of said carbonaceous binder for said carbonaceous solids, subjecting said solid residue to low temperature carbonization to produce char and tar, and introducing at least a portion of said char into said kiln to serve as at least part of said carbonaceous solids.

3. The process according to claim 2 wherein said solvent is a middle distillate fraction of the tar produced in the process itself.

4. The process of claim 2 wherein all the coal fed to the process is subjected to said solvent treatment.

5. In the process of making agglomerates from a weakly or noncaking coal wherein a mixture of carbonaceous solids and carbonaceous binder is tumbled in a rotary kiln to yield agglomerates and tar, there being an inadequate amount of the requisite carbonaceous binder produced autogenously in said kiln, the improvement comprising dividing the coal fed to the process into three portions, feeding one portion directly to said rotary kiln, subjecting the second portion to treatment with a solvent at an elevated temperature to yield a solid residue and a coal extract containing a nondistillable fraction which is fluid at the forming temperature in the kiln, introducing said nondistillable coal extract fraction into said kiln to serve as at least part of said carbonaceous binder for said carbonaceous solids, subjecting the third portion of the feed coal to low temperature carbonization to yield char and tar, and introducing at least some of the char into said rotary kiln to serve as at least part of said carbonaceous solids.

6. The process according to claim 5 wherein said solid residue is subjected to low temperature carbonization to produce char and tar; and at least a portion of said char is introduced into said rotary kiln.

7. The process according to claim 6 wherein said solvent is a middle distillate fraction of the tar produced in the process itself.

8. The process according to claim 6 wherein at least part of the char produced in the process is rejected Without going through said rotary kiln.

References Cited UNITED STATES PATENTS NORMAN YUDKOFF, Primary Examiner 0 D. EDWARDS, Assistant Examiner US. Cl. X.R. 

